Hot gas defrosting means for refrigerating systems



March 24, 1953 v. w. SMITH 2,632,303

HOT GAS DEFROSTING MEANS FOR REFRIGERATING SYSTEMS Filed Aug. 9, 1949 2SHEETS-SHEET l INVENTOR. W6 70/? W SM/Th BY MM March 24, 1953 v, w.sMlTH 2,632,303

HOT GAS DEFROSTING MEANS FQR REFRIGERATING SYSTEMS Filed Aug. 9, 1949 2SHEETS-SHEET 2 INVEN TOR. V/CTOR W. SM/TH ,4 TTOR/VEY Patented Mar. 24,1953 UNITED STATES HOT GAS DEFRGSTING MEANS FDR REFRIGERATING SYSTEMSVictor W. Smith, TrentonQN. J., assignor to C. V.

Hill & Company, Inc., Trenton, N. .L, a corporation of New JerseyApplication August 9, 1949, Serial No. 109,335

8 Claims.

This application is a continuation-in-part of my copending applicationSerial No, 752,031 filed June 3, 1947., now Patent No. 2,555,161, May29, 1951.

The present invention relates to refrigerating systems of the typewherein a compressor, condenser and evaporator are connected in series,and is directed particularly to systems including means for supplyinghot refrigerant gas to the evaporator to heat the evaporator fordefrosting or other purposes.

The possibility of using hot refrigerant gas from the compressor fordefrosting the evaporator has been recognized for over fifty years butsysterns employing such a principle have never been employed extensivelyfor the reason that the re- 'frigerant is largely condensed to a liquidin the evaporator during the defrosting operation as it gives up heat tomelt the ice on the coil and fins f the evaporator. The refrigerantreturning to the compressor therefore is largely in the form of liquidwhich the compressor is not equipped to handle and which causes thecompressor to knock and may break valves, stall the motor, or causeother serious injury to the equipment. Moreover, when the condenser andexpansion valve are bypassed the refrigerant flows freely from the highside of the compressor, through the evaporator and back to the low sideof the "compressor. The load is thus reduced so that the compressorraces and performs insufficient work on the gaseous refrigerant to raiseits temperature enough for efiective defrosting.

In an attempt to overcome such practical obstacles to successfulapplication of the principle of hot gas defrosting, restricting valveshave been located between the evaporator and compressor to impose a loadand reduce the pressure on the intake side of the compressor duringdefrosting. This prevents racing of the compressor when defrosting butliquid refrigerant still flows past the restricting valve to thecompressor, since little or no heat input for vaporization of thecondensed refrigerant can take place between the restricting valve andthe compressor. Moreover, when the restrictor is itself by-passed duringthe normal refrigerating operation it is necessary to employ additionalvalves which complicate the system and often give rise to surging ofliquid refrigerant into the compressor when the restrictor is out in orout out of the circuit. Furthermore if the re'strictor'used isresponsive to the pressure in the evaporator vigorous surging occurs atthe conclusion of the defrosting cycle when the restrictor is renderedinoperative or ;bypassed and large amounts of liquid refrigerant 2 areadmitted to the warm evaporator by the regular expansion valve.

Systems also have been proposed wherein heat accumulators and electricalheating elements are provided for vaporizing the condensed refrigerantpassing from the evaporator to the compressor. However, when such heatis supplied by accumulators the amount of stored heat available forrevaporizing the refrigerant is limited so that when the defrostingoperation is prolonged the accumulated heat is expended and the devicebecomes inoperative.- On the other hand when means such as an electricalheating element are used to revaporize the refrigerant thepowerconsumption of the system is prohibitive since the heat input necessaryto insure such revaporizae tion must be equal to the heat expended bythe gaseous refrigerant when it condenses in defrost ing the evaporator.

In accordance with the present invention these objections to priorrefrigerating systems are overcome and a system of thecompressor-condenserevaporator type is provided with defrosting meanswhich are efficient and inexpensive to operate and which at'the sametime impart to the system a wholly new characteristic in that itfunctions as a stabilizing means which prevents surging of therefrigerant in the lines and prevents over-cooling of the space in whichthe evaporator is located. These results are preferably attained byemploying restricting means and re-evaporating means in combination andcontinuously maintained in the refrigerating circuit between theevaporator and the compressor. The elements of the combination furtherare designed and organized so as to insure complete vaporization ofrefrigerant returning to the evaporator andto eliminate surging,trapping or short circuiting of the refrigerant or entrained oil inIcy-pass lines or elsewhere in the system.

In accordance With the present invention heat required forre-vaporiz'ing refrigerant condensed during the defrosting operation isderived from a constant and unlimited source of heat supply such as theambient air. The defrosting operation can then be continued aslongas'required so as to eliminate all frost from theevaporator. Moreover,when desired heat may be supplied to the evaporator after completion ofthe defrosting operation and for a further period of time to raise thetemperature of the space in which the evaporator is located. In this waythe system may be employed as a temperature stabilizing means formaintaining a-space at substantially constant and predeterminedtemperatures under varying conditions of use.

One of the objects of the present invention is to provide a novel typeof refrigerating system wherein hot gas defrosting means are employed incombination with a restricting means and a re-evaporator continuouslymaintained in the refrigerating circuit;

A further object of the invention is to provide a hot gas defrostingsystem wherein a re-evaporator is provided with an unlimited supply ofheat for vaporizing liquid refrigerant returning to the compressor.

Another object of the invention is to. provide a refrigerating systemhaving hot. refrigerant. defrosting means designed andv organized toeliminate surging of refrigerant in the system.

A further object of the invention is to provide a refrigerating systemcapable of functioning as a temperature stabilizing system.

These and other objects and features of the present invention willappear from the following description thereof in which reference is madeto the figures of the accompanying drawings.

In the drawings:

Fig. 1 is a diagrammatic illustration of a typical system embodying thepresent invention;

Fig. 2 is a vertical sectional view through a typical refrigerateddisplay case embodying the present invention; I

Fig. 3 is a vertical sectional view through a refrigerated display caseillustrating an alternative embodiment of the present invention;

Fig. 4 is an enlargedlsectional view of a constant pressure valveadapted for. use in the system illustratedin Figs. 1 and 3;

Fig. 5 is a perspective of a preferred form of re-evaporator employed inthe practice of the present invention; and

Fig. 6 is a diagrammatic illustration of an alternative form ofrestricting valve assembly.

In that form of the invention illustrated in the drawings therefrigerating system embodies a compressor 2, a condenser 4, and anevaporator t. The compressor is driven by a motor 8. During normalrefrigerating operation the refrigerant is passed from the compressor 2to the condenser through the high pressure line Ill and conduit l2. Inthe condenser the hot refrigerant gas is cooled and condensed from avapor to a liquid. The liquid refrigerant passes to a receiver it fromwhich it flows to the evaporator 6 through conduit 16 and. enters theevaporator through an expansionvvalve [,8 controlled by the temperatureresponsive. bulb. is located near the outlet from the evaporator. Therefrigerant on passing the expansion valve is. vaporized in theevaporator drawing heat from air in the chamber 20 in which theevaporator is located. The vaporized refrigerant from the evaporator isthereafter returned to the compressor during the refrigerating cyclethrough the conduit 22, restrictor 24, re-evaporator 2'6, and returnline 28.

For defrosting purposes the system is provided with a by-pass conduitwhich serves to conduct hot refrigerating gas from the compressor 2 tothe evaporator B at apoint adjacent butbeyond the expansion valve I8.For this purpose the by-pass conduit 30 isconnected to the high pressureline I0 between the compressor and the condenser and is provided with avalve 32 which preferably is actuated by means of a solenoid 3t undercontrol of actuating means 36 such as a time clock, thermostat, or othercontrol device. When the actuating means operates to open the valve 32both the condenser 4 and theexpansion valve [8 are by-passed and the hotcompressed refrigerant gas flows directly from the compressor 2 to thecoils of the evaporator 6. Frost which has accumulated on the coils andfins of the evaporator is then melted rapidly so that the evaporator isdefrosted in a very short time. The heat given up by the hotgas inctheevaporator causes the refrigerant; to condense into a liquid so thatliquid refrigerant flows from the evaporator through conduit 22 to therestrictor 2a.

The restrictor 24 and re-evaporator 26 are continuously connected inseries between the evaporator and compressor, The restrictor isresponsivev to a condition of the refrigerant passing to the intake sideof the compressor such as the pressure or temperature of the returningrefrigerant gas.

In practice it is generally preferable to employ a pressure responsivevalve which imposes very limited restriction to the flow of refrigeranttherethrough under the low pressure conditions of the refrigeratingcycle but effectively restricts such flow and acts as an expansion valveunder the high pressure conditions of the defrosting cycle. The valveshown in Fig. 4 is of this type and is provided with an inlet port 38,an outlet port 9 and a main valve member 42 loosely fitted within thevalve body and urged toward valve seat id by spring 46. A suctionpassage 58 extends from a point adjacent the outlet port it to a chamber50 above a secondary valve seat member 52. A side passage 54 extendsfrom suction passage 48 to the central opening 56 in member 52 wherein asecondary valve member 59 is movable. The latter valve member is helddepressed under low pressure, conditions of operation by the diaphragm62 engaged by spring 5 5. At such times the secondary valve member 6%remains open and suction created at the outlet port of the valve, by theintake of the compressor is exerted on the upper surface of the mainvalve member 42 whereby the valve mem her is raised against the actionof spring it. In this Way the restrictor operates to permit ready flowof refrigerant from the inlet port 38 to the outlet port 40 during therefrigerating cycle.

There is an increase in pressure at the outlet port 40 of the valve assoon as the defrosting cycle starts due to by-passing of expansion valvel8, and direct flow of liquid refrigerant to the evaporator. Thepressure at the outlet side of valve 2 1 then rises whereupon thediaphragm 52 is raised against the action of spring 64 and the secondaryvalve member then closes under the action of springtt. Thereafter, thepressure on opposite sides of. main valve member :42 is equalized byflow of refrigerant through the small port 63 in the side wall of thmain valve member and into the space beneath the valve seat member 52.The valve member then is urged toward open position only by the pressureof refrigerant adjacent, inlet port 38. and acting against spring 45.The restrictor then acts as a throttle or expansion valve for limitingthe flow of the refrigerant to the re-evaporator and compressor.

In this way an adequate difference in pressure is maintained on oppisitesides of the compressor at all times so as to insure uniformity ofoperation which maintains a suitable load on the compressor and preventracing of the motor. At the same time by locating the restrictor 24close to, and in advance of, the re-evaporator 25 the restrictor acts asan expansion valve during the defrosting cycle.- The re e aporatcr hen oe ates as an evaporator, whereas the evaporator 6 then functions as acondenser or heat dissipating means during the defrosting cycle.

The valve 2 3 further operates to overcome the surging which tends tooccur when the refrigerating cycle is first renewed. The evaporator B atthat time is relatively Warm and the bulb I!) at the outlet of theevaporator therefore causes the expansion valve iii to admit the maximumamount of liquid refrigerant to the evaporator. If restrictor 24 ispositively opened or by-passed under such conditions the rapidvaporization of liquid refrigerant in the evaporator will force anyliquid remaining in the line directly into the compressor. However, therestrictor of Fig. 4, being responsive to pressure, precludes suchsurging and limits the flow of refrigerant to the compressor.

Various forms of coils or expansion chambers may be used as there-evaporator 25 but as shown in Fig. 5 the re-evaporator preferablyembodies a pipe 65 extending from restrictor 24 to an inlet header 66.Two coils ill extend in parallel from inlet header 55 to an upper header68. A return pipe 69 carries the refrigerant from upper header 68 to asecond lower header Hi from which two coils extend in parallel to theoutlet header i2 connected to return line 23 leading to the intake orlow pressure side of the compressor. The coils of the re-evaporator areprovided with the usual fins 74 and are mounted within a casing 56having openings 78 in opposite sides thereof through which air iscirculated. Because of the multiple passages provided for the flow ofrefrigerant through the re-evaporator the device has a relatively largecapacity and offers an extended area for heat exchange without imposingrestrictions or back pressure on the system during the normalrefrigeration cycle. At the same time a large pressure drop of therefrigerant within the re-evaporator is provided during the defrostingcycle by reason of the restrictor 24 thereby insuring expansion andcomplete vaporization of the condensed liquid refrigerant passing fromthe evaporator to the compressor during the defrosting cycle. Thus whenoperating on the defrosting cycle the evaporator acts as a condenser orheat discharging element whereas the re-evaporator acts as an evaporatoror heat absorbing element.

The restrictor 24 and re-evaporator 2B are continuously maintained inthe circuit including the evaporator and compressor and therefore thesystem is very simple in construction and eliminates many of the valvesandby-pass conduits used in prior systems employing hot gaseousrefrigerant for defrosting purposes. Moreover, by constructing theevaporator so that its capacity and heat exchanging surface equal ormore of the capacity and heat exchanging surface of the evaporator orcondenser it is found to function as a further surge eliminator duringthe transition of the system to and from the refrigerat ing cycle andthe defrosting cycle. The reevaporator then acts as an expansion chamberand receiver which retains all liquid refrigerant passing the restrictoruntil the refrigerant has vaporized completely. Slugs of liquidrefrigerant therefore cannot reach the compressor and a continuous andrelatively even flow of refrigerant gas returning to the compressor ismaintained.

In order to supply the re-evaporator with the necessary heat units forvaporizing'the refrigerant a fan 80 is located adjacent one of theopenings I8 in the casing "5. Air at a tempera.- ture above the boilingpoint of the refrigerant is thereby passed over the coils and fins.There is no limit as to the amount of air that can be circulated throughthe casing and over the coils and fins of the re-evaporator and sincethe air is constantly renewed and is always at a tem perature above theboiling point of any conventional refrigerant used it aifords anunlimited supply of heat for transfer to the refrigerant beingvaporized. Therefore the defrosting cycle can be continued as long asdesired without expense other than the cost of operating the fan 80.

In the illustrations of the present invention embodied in Figs. 2 and 3the refrigerating and defrosting means are employed for maintaining thedesired temperatures in an open top self service refrigerated displaycase of the type frequently used in the sale of frozen foods. Therefrigerated space or chamber is indicated at $20 and air is circulatedover the evaporator 6 and through the space 2 by means of the blower 82.The evaporator E is located at the rear and above the re frigerateddisplay space 22!} and the direction of flow of air within the displayspace is indicated by the arrows in Fig. 2. Since the temperature of thedisplay space and of the air circulated therethrough and over the coilsof the evaporator is maintained below freezing it will be apparent thatdefrosting of the evaporator normally would not take place withoutraising the temperature of the air in space 29 above 32 F., the meltingpoint of the frost on the coils. Such a rise in temperature would beruinous to frozen foods whereas the present invention effects defrostingof the evaporator almost instantly and without material rise intemperature of the air in the refrigerated space 2%).

In the construction shown in Fig. 3 the compressor and condenser arelocated in the basement of the building, and the re-evaporator is housedwithin the cabinet but in the open base thereof beneath the refrigerateddisplay space 2i. Air for supplying heat to the liquid refrigerant inthe re-evaporator is therefore drawn from the room in which the displaycase is located, and since this air circulates freely within the storeor room the supply of heat to the re-evaporator from the ambient air isunlimited.

Even when the air circulated over the reevaporator is drawn from a spacerefrigerated by the evaporator it is necessarily at a temperature abovethe boiling point of the refrigerant. Thus as shown in Fig. 2 at least aportion 84 of the reevaporator coils '85 may be located within therefrigerated space 28 which is cooled by the evaporator 6 during therefrigerating cycle. In such installations the air circulated over theportion 8d of the rte-evaporator is cold but still is at a temperatureabove the boiling point of any conventional refrigerant and therefore iscapable of supplying heat to the coils 34 in amounts sufficient tore-vaporize the liquid refrigerant received from the evaporator.Moreover, additional coils 86 of the ire-evaporator may be locatedexteriorly of the refrigerated chamber '28 and supplied with heat fromthe ambient air by a fan 88 if desired. The coils 'S i of there-evaporator in such installations serve to refrigerate the air withinthe space 29 while the evaporator 6 is being defrosted and thuscompensates for heat losses through the walls of the case and to someextent at least for the sensible heat input to the air adjacent the thenheated evaporator =6.

In this way the temperature of the air within a refrigerated space canbe maintained substantially constant even during the defrosting cycleand temperature rise can be reduced or avoided altogether. Moreover, thedefrosting cycle can be continued as long as desired or necessary toinsure removal of all ice and frost from the coils and fins of theevaporator. In fact the defrosting cycle can be continued indefinitelyand used to maintain substantially constant temperatures in an enclosureunder special or unusual conditions of operation. Thus during a severewinter or in arctic climates it is sometimes desirable to preventover-cooling or freezing of articles such as vegetables or eggs, forexample, or to avoid long periods for the thawing of refrigerated meatsand other products. With the present invention, even though the ambienttemperature is well below zero or at any temperature above the boilingpoint of the refrigerant, the defrosting cycle may be prolonged or madea continuous cycle whereby the re-evaporator operates continuously as anevaporator and the evaporator functions continuously as a heatdischarging element over which. air may be circulated to produes ormaintain a desired and controlled temperature Within a chamber. Thistemperature stabilizing action of the present invention gives to thesystem an important function not heretofore attainable with priorsystems using hot refrigerant gas for defrosting purposes.

The means employed for controlling operation of the b -pass valve 52 forinitiating and terrnihating the defrosting operation may varyconsiderably. In practice it has been usual to em ploy a time clock withelectrical circui s for energizing a solenoid to initiate the defrostinoperation periodically and to terminate the defrosting operation after apredetermined time. However, as described in the co-pending applicationc-f Mach-faster, Serial No. 565,912, filed April 20, 1%6, the defrostingoperation may be initiated by time controlled means and may beterminated by pressure responsive means upon a rise in pressure of therefrigerant gas in the evaporator due to completion of the defrostingoperation and subsequent lack of condensation of the refrigerant in theevaporator. When the system is employed. as a temperature stabilizingmeans wherein the evaporator may operate for considerable periods oftime as an element for supplying heat to the refrigerated space, thebypass valve 32 may be controlled by a thermostat or many other suitablemeans. Thus it will be apparent that the system lends itself to variousapplications and provides a simplified and smoothly operating systemhaving dual characteristics in that defrosting and temperature controlor stabilizing can be effected by suitable control and operation of theby-pass valve 32.

The restrictor 24 used in combination with he reheater also may bevaried, and as shown in Fig. a temperature responsive expansion valve 90may be used and may be controlled by the temperature of the refrigerantpassing from the outlet side of valve Ell to the re-evaporator 2 5. Forthis purpose a bulb 92 is placed adjacent the line connecting valve soto the re-evaporator and supplied with an expanding fluid for actuatingthe valve. In this construction the flow of relatively warm condensedliquid through valve 98 Will cause the valve to close and operate as anexpansion valve whereas the flow of expanded and cooled refrigerant gasfrom the evaporator to valve 90 will serve to hold the valve open toreduce restriction to flow of refrigerant gas to the compressor. Othertypes of, restricting means or valves responsive to the condition ofrefrigerant on the compressor side of the restricting means may beemployed. Similarly the form and type of re-evapo-rator coils may bevaried to adapt the invention to different applications. Other changesalso may be made in the construction and arrangement of elements used inthe system and in view thereof it should be understood that thparticular form of the invention shown in the drawings and hereindescribed are intended to be illustrative only and are not intended tolimit the scope of the invention.

I claim:

1. In a refrigerating system having a compressor, a condenser and anevaporator connected by conduit means, together with a controlled bypassconduit for conducting refrigerant from the compressor to the evaporatorso as to by-pass the condenser for defrosting the evaporator, thecombination of additional conduit means providing a single passage forreturn of refrigerant from said evaporator to the compressor, saidadditional conduit means having a restrictor and a rte-evaporatorcontinuously connected in series therein between said evaporator andcompressor whereby all of the refrigerant returning to the compressorduring both the refrigerating and defrosting cycles of operation iscaused to flow through said re-evaporator, said restrictor beingresponsive to a condition of refrigerant flowing from the evaporatortothe compressor to impose relatively limited restriction to such flowduring the refrigerating cycle and to function as an expansion valveduring the defrosting operation, and means for circulating air at atemperature above the boiling point of the refrigerant in heatexchanging relation with said re-evaporator.

2. In a refrigerating system having a compressor, a condenser and anevaporator connected by conduit means, together with a controlled bypassconduit for conducting refrigerant from the compressor to the evaporatorso as to by-pass the condenser for defrosting the evaporator, thecombination of additional conduit means provid ing a single passage forreturn of refrigerant from said evaporator to the compressor, saidadditional conmit means having a restrictor and a re-evaporatcrcontinuously connected in series therein between said evaporator andcompressor whereby all of the refrigerant returning to the compressorduring both the refrigerating and defrosting cycles of operation iscaused to flow through said ire-evaporator, said restrictor consistingof a valve responsive to pressure adjacent the compressor side thereofto impose relatively little restriction to the flow of refrigeranttherethrough during the refrigerating cycle and to function as anexpansion valve during the defrosting cycle, and a blower forcirculating air at a temperature above the boiling point of thererigerant in heat exchanging relation with said re-evaporator.

3. in a refrigerating system having a compressor, a condenser and anevaporator connected by conduit means, together with a controlled bypassconduit for conducting refrigerant from the compressor to the evaporatorso as to icy-pass the condenser for defrosting the evaporator, thecombination of additional conduit means provid ing a single passage forreturn of refrigerant from said evaporator to th compressor, said.additional conduit means having a restrictor and a, i s-evaporatorcontinuously connected in series therein between said evaporator andcompressor whereby all of the refrigerant returning to the compressorduring both the refrigerating and defrosting cycles of operation iscaused to flow through said re-evaporator, said restrictor consisting ofa pressure responsive valve including a valve member movable in responseto relatively low pressure on the compressor side of the valve to imposerelatively slight restriction to the flow of refrigerant through saidvalve and movable upon an increase in pressure on the compressor side ofthe valve to impose a relatively greater restriction to flow ofrefrigerant therethrough, and a blower for circulating air at atemperature above the boiling point of the refrigerant in heatexchanging relation with said re-evaporator.

4. In a refrigerating system having a compressor, a condenser and anevaporator connected by conduit means, together with a controlled bypassconduit for conducting refrigerant from the compressor to the evaporatorso as to by-pass the condenser for defrosting the evaporator, thecombination of additional conduit means providing a single passage forreturn of refrigerant from said evaporator to the compressor, saidadditional conduit means having a restrictor and a re-evaporatorcontinuously connected in series therein between said evaporator andcompressor whereby all of the refrigerant returning to the compressorduring both the refrigerating and defrosting cycles of operation iscaused to flow through said re-evaporator, said re-evaporator presentinga cross sectional area for the flow of refrigerant exceeding the crosssectional area of the conduit means in advance thereof, and means forcirculating air at a temperature above theboiling point of therefrigerant in heat exchanging relation with said re-evaporator.

5. In a. refrigerating system having a compressor, a condenser and anevaporator connected in a closed circuit by conduit means, together with"a controlled by-pass conduit for conducting refrigerant from thecompressor to the evaporator for defrosting the evaporator, thecombination of a restrictor and a re-evaporator connected in series andcontinuously included in said circuit between the evaporator and thecompressor whereby all of the refrigerant returning to the compressorduring both the refrigerating and defrosting cycles of operation iscaused to flow through said re-evaporator, said evaporator being locatedwithin a space to be refrigerated, at least a portion of saidre-evaporator being located in heat exchanging .relation with air insaid space, and means for circulating air at a temperature above theboiling point of the refrigerant in heat exchanging relation with saidre-evaporator.

6. In a refrigerating system having a compressor, a condensor and anevaporator connected in a closed circuit by conduit means, together witha controlled by-pass conduit for conducting refrigerant from thecompressor to the evaporator for defrosting the evaporator, thecombination of a restrictor and a re-evaporator connected in series andcontinuously included in said circuit between the evaporator and thecompressor whereby all of the refrigerant returning to the compressorduring both the refrigerating and defrosting cycles of operation iscaused to flow through said means for circulating air from said space inheat exchanging relation with said portion of said re-evaporator.

7. In a refrigerating system having a compressor, a condenser and anevaporator connected in a closed circuit by conduit means, together witha controlled by-pass conduit for conducting refrigerant from thecompressor to the evaporator for defrosting the evaporator, thecombination of a restrictor and a re-evaporator connected in series andcontinuously included in said circuit between the evaporator and thecompressor whereby all of the refrigerant returning to the compressorduring both the refrigerating and defrosting cycles of operation iscaused to flow through said rc-evaporator, said evaporator being locatedwithin a space to be refrigerated and said reevaporator being located onthe exterior of said space, means for circulating air from the exteriorof said space over said re-evaporator, there being only three valves insaid conduits, namely an expansion valve in said conduit means betweenthe condenser and the evaporator, a h y-pass valve in said by-passconduit, and a pressure responsive Valve functioning as the restrictorduring the defrosting cycle and rendered relatively inactive by areduction in pressure of refrigerant passing to the compressor duringthe refrigerating cycle.

8. Ina refrigerating system havin a compressor, a condenser and anevaporator connected by conduit means, together with a controlled bypassconduit for conducting refrigerant from the compressor to the evaporatorso as to by-pass the condenser for defrosting the evaporator, thecombination of additional conduit means providing a single passage forreturn of refrigerant from said evaporator to the compressor, saidadditional conduit means having a restrictor and a re-evaporatorcontinuously connected in series therein between said evaporator andcompressor whereby all of the refrigerant returning to the compressorduring both the refrigerating and defrosting cycles of operation iscaused to flow through said re-evaporator, said re-evaporator includingan inlet header and an outlet header with a plurality of coils extendingin parallel relation from said inlet header to said outlet header, andmeans for circulating air at a temperature above the boiling point ofthe refrigerant in heat exchanging relation with said reevaporator.

VICTOR W. SMITH.

REFERENCES CITED The following references are of record in the file ofthis patent:

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